Integrated capacitor transimpedance amplifier

ABSTRACT

Spectrometers including integrated capacitive detectors are described. An integrated capacitive detector integrates ion current from the collector ( 220 ) into a changing voltage. The detector includes a collector configured to receive ions in the spectrometer, a dielectric ( 228 ), and a plate ( 232 ) arranged in an overlapping configuration with collector on an opposite side of the dielectric. The detector also includes an amplifier ( 226 ).

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a detector apparatus and moreparticularly to detectors for spectrometers.

Ion mobility spectrometers (“IMS”) and field asymmetric ion mobilityspectrometers (“FAIMS”) or differential mobility spectrometers (“DMS”)apparatus are often used to detect substances such as explosives, drugs,blister and nerve agents or the like. A spectrometer typically includesa detector cell to which a sample of air containing a suspectedsubstance or analyte is supplied as a gas or vapor. The cell operates ator near atmospheric pressure and contains electrodes energized toproduce a voltage gradient along the cell.

Molecules in the sample of air are ionized, such as by means of aradioactive source, an ultraviolet (“UV”) source, or by coronadischarge, and are admitted into the drift region of the cell by anelectrostatic gate at one end. The ionized molecules drift to theopposite end of the cell at a speed dependent on the size of the ion toa collector, which causes a current pulse in the collector. The currentinto the collector is converted to a voltage and amplified. By measuringthe time of flight along the cell it is possible to identify the ion.

The subject matter discussed in this background of the invention sectionshould not be assumed to be prior art merely as a result of its mentionin the background of the invention section. Similarly, a problemmentioned in the background of the invention section or associated withthe subject matter of the background of the invention section should notbe assumed to have been previously recognized in the prior art. Thesubject matter in the background of the invention section merelyrepresents different approaches, which in and of themselves may also beinventions.

SUMMARY OF THE INVENTION

Spectrometers including integrated capacitive detectors are described.The spectrometers can be used to ionize molecules from a sample ofinterest in order to identify the molecules based on the ions. In animplementation, the ions travel along a chamber within a spectrometerand are collected by a collector. The ion signal produced is amplifiedby the integrated capacitive detector.

In one aspect, a spectrometer is provided. The spectrometer includes adetector. The detector includes a collector with a first side configuredto receive ions that have drifted toward the collector and a secondside. The detector also includes a dielectric element proximate thesecond side of the collector. The detector also includes an amplifierwith an input and an output. The detector also includes a capacitiveplate element proximate the dielectric element and opposite thecollector. The capacitive plate element is coupled with the output ofthe amplification element.

In another aspect, a spectrometer is provided. The spectrometer includesa detector. The detector includes a collector configured to receive ionsthat drifted toward the collector supported on a first side of adielectric. The detector also includes a plate element disposed on asecond side of the dielectric opposite the first side in an overlappingconfiguration with collector. The detector also includes an amplifierhaving an input and an output. The collector is electrically coupledwith the input. The plate element is electrically coupled with theoutput.

Another embodiment of the invention relates to a spectrometer. Thespectrometer includes a collector configured to collect ions. Thecollector is arranged and configured as a first plate of a capacitor.The spectrometer also includes a dielectric proximate the collector. Thespectrometer also includes a plate configured as a second plate of acapacitor arranged opposite the collector relative to the dielectric.The spectrometer also has an amplification element including an input,an output, and a feedback loop. The capacitor is configured in thefeedback loop.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentify the figure in which the reference number first appears. The useof the same reference number in different instances in the descriptionand the figures may indicate similar or identical items.

FIG. 1 is a schematic illustration of an exemplary IMS apparatusincluding an integrated capacitive detector in accordance with anembodiment of this disclosure;

FIG. 2 illustrates a detailed view of an embodiment of an integratedcapacitive detector that may be utilized, for example, as an integratedcapacity detector with the exemplary IMS apparatus illustrated in FIG.1;

FIG. 3 is a schematic illustration of an embodiment of a transimpedanceamplifier circuit, such as, for example, a circuit formed by thearrangement illustrated in FIG. 2;

FIG. 4 is a schematic illustration of an alternate embodiment of thecircuit formed by the arrangement illustrated in FIG. 2;

FIG. 5 is a schematic illustration of a second embodiment of an IMSapparatus including an integrated capacitive detector and a seconddetector; and

FIG. 6 is a schematic illustration of an embodiment of a detector with areset circuit.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a schematic illustration of an exemplary spectrometer, such asan ion mobility spectrometer (“IMS”) 100 that implements electricalionization of molecules in a sample of interest. The IMS 100 includes anelongate housing 102 extending from a first wall 104 to a second wall106. Defined in the housing 102 proximate the first wall 104 is an inlet108. Molecules of interest may be drawn into the housing 102 through theinlet 108. The housing 102 also defines an ionization chamber 110 and adrift chamber 112 in fluid communication but separated by a gate 114that can control passage of ions to the drift chamber 112. Theionization chamber 110 includes an ionization source 116, which may be aradioactive source, such as a nickel 63 source, a corona dischargedevice, a photoionization source, or any other suitable type of sourcefor ionizing the sample of interest. The drift chamber 112 includeselectrode pairs 118 spaced along the drift chamber 112 to provide apotential gradient along the length of the drift chamber 112 that iseffective to cause ions to drift from left to right (as shown in FIG.1). Proximate the second wall 106 of the housing 102 in the driftchamber 112 is a collector 120 of a detector 122. Ions are detected asthe ions come in contact with the collector 120.

Ionization of the molecules of interest can occur in a variety of ways.For example, an ionization source can ionize a molecule through variousmultistep processes using ions that are formed in the plasma.

In embodiments, reactant ions are generated by a corona. The reactantions ionize the molecule of interest. For example, the ionization sourceforms ions that are subsequently drawn away to ionize the molecules ofinterest. Reactant ions may be ionized gases (e.g., nitrogen and gasesin air) and other gases in the ionization chamber, such as water, and soforth. Although fragmentation of the molecule of interest is possible,ionization can be controlled to result in “soft” ionization therebyminimizing fragmentation of the molecule in favor of the moleculecarrying a single charge, e.g., a plus one or minus one charge.

In one embodiment, the IMS times how long it takes an ion to reach thecollector 120 after the gate 114 is opened. This time-of-flight can beassociated with the underlying molecule. The ion's ion mobility is usedto identify the molecule associated with the ion. For example, acomputer can be used to compare the detector's 122 output with a libraryof plasmagrams of known ions. The ion current discharged from thecollector 120 is typically very small. Therefore, as will be describedfurther below, the detector 122 includes an amplification circuit 124including an amplification element 126 to amplify the ion current.

The output of the detector 122 may be coupled to a measuring system 123.Embodiments of measuring systems 123 may include analog-to-digitalconverters, digital-to-analog converters, amplification elements,processors, etc., as will be further explained below. Processors are notlimited by the materials from which they are formed or the processingmechanisms employed therein. For example, the processor may be comprisedof semiconductor(s) and/or transistors (e.g., electronic integratedcircuits (“IC's”)). Embodiments may include other suitable measuringsystem 123.

Memory can be included with the processor. Memory can store data, suchas a program of instructions for operating the IMS, data, and so on.Although a single memory device can be used, a wide variety of types andcombinations of memory (e.g., tangible memory) may be employed, such asrandom access memory (“RAM”), hard disk memory, removable medium memory,external memory, and other types of computer-readable storage media.

Ions move down the drift chamber 112 towards the second wall 106.Located proximate the second wall 106 is the collector 120. In theillustrated embodiment, the collector 120 is supported by a dielectric128. The dielectric 128 may be any suitable dielectric, and in theillustrated embodiment is a printed circuit board (“PCB”) composed ofpolyimide. The collector 120 may be composed of any suitable material(e.g., copper, other metals, conductive materials, etc.) or combinationof materials and may be deposited on the PCB or coupled with the PCB bysuitable means.

FIG. 2 illustrates a detailed view of an embodiment of an integratedcapacitive detector that may be utilized, for example, as an integratedcapacity detector with the exemplary IMS apparatus illustrated inFIG. 1. The collector 220 is deposited on the PCB 228 over a suitablearea for collecting ions. In one embodiment, the PCB 228 issubstantially circular with a diameter of approximately 7.5 millimetersand a square area of approximately 44 square millimeters. Other suitableshapes, dimensions, and areas are also envisioned. In one embodiment,the collector 220 is of a size that is sufficiently compact whilepermitting accurate detection. In the illustrated embodiment, thecollector 220 is surrounded by a guard ring 230. The guard ring 230 maybe formed from any suitable material, such as a conductive material,metal, or the like.

Supported on the side of the PCB 228 opposite the collector 220 is acapacitive plate element 232. The capacitive plate element 232 may becomposed of any suitable material (e.g., copper, other metals,conductive materials, etc.) or combination of materials and may bedeposited on the PCB or coupled with the PCB by suitable means.

A parallel plate capacitor has a capacitance based on the overlappingsurface area of the plates, the separation between the plates, and thedielectric constant (relative permittivity) according to the equation

C=(k*8.854*10⁻¹² *A/D)*1*10⁻¹²

where k is the dielectric constant of the dielectric material, A is theoverlapping area of the plates, D is the distance between the plates,and C is the capacitance of the capacitor.

The overlapping portions of the capacitive plate element 232 and thecollector 220, along with the PCB 228 are configured to act as acapacitor, with the portion of the collector 220 overlapping thecapacitive plate element 232 acting as one of the plates of a capacitorand the PCB 228 acting as the dielectric, and the capacitive plateelement 232 acting as the other plate of a capacitor. The capacitiveplate element 232 is dimensioned to have an area overlapping a portionof the area of the collector 220 to achieve a desired capacitance for adesired application, as will be further described below. In oneembodiment, the PCB 228 is formed from polyimide, which has a delectricconstant of approximately 3.4. The capacitive plate element 232 is sizedto have approximately 44 square millimeters of area overlapping thecollector 220. The PCB 228 is approximately 1.5 millimeters thick. Thus,the capacitance of the capacitor formed by the collector 220, thecapacitive plate element 232, and the PCB 228 is approximately 0.883picoFarads. Other arrangements resulting in other capacitances suitablefor various applications are also envisioned.

As will be explained further below, the capacitor formed by theoverlapping portions of the capacitive plate element 232 and thecollector 220 along with the dielectric and the collector 220 form asumming junction node of a capacitive transimpedance amplifier circuit.This summing junction node is coupled with a first input 234 of theamplification element 226.

With further reference to FIG. 2, the amplification element 226 is anoperation amplifier of any suitable type. Additionally, other suitabletypes of amplification elements are also envisioned. The first input 234of the operational amplifier 226 is its inverting input. The operationalamplifier 226 also includes a second input 236, which is thenon-inverting input of the operational amplifier 226. The second input236 of the operational amplifier 226 is grounded. The operationalamplifier 226 also includes an output 238. The output 238 is coupledwith the capacitive plate element 232.

FIG. 3 is a schematic illustration of the circuit formed by theapparatus illustrated in FIG. 2. The capacitor formed by the capacitiveplate element 232, the dielectric 228, and the collector 229 of FIG. 2functions as a feedback capacitor 340 disposed in a feedback loop of theamplification element 326. The feedback capacitor 340 and the collector320 meet at a summing junction node 342 which is coupled with theinverting input 334 of the operational amplifier 326.

The circuit of FIG. 3 functions as a capacitive transimpedance amplifierthat converts current applied to its input to a low impedance output. Asions impact the collector 320, this ion signal causes charge toaccumulate across the capacitor 340 and the output of the operationalamplifier 326 increases in the positive or negative direction dependenton the polarity of the input signal. Thus, the circuit, as illustrated,operates as an integrator and integrates the ion current from thecollector 320 as an increasing voltage.

As the charge accumulates on the capacitor 340, the capacitor 340 mayreach its operational limit, requiring discharging to reset thecapacitor 340. In one embodiment, the capacitor 340 is coupled inparallel with a resetting switching circuit 344.

When it is desired to reset the capacitor 340, the switch of theresetting switching circuit 344 may be closed, allowing the capacitor340 to be reset and discharge. In embodiments, the resetting switchingcircuit 344 may also contain resistive elements to control the rate ofchange of voltage to limit instantaneous current.

FIG. 4 is a schematic illustration of the circuit formed by theapparatus illustrated in FIG. 2 with an alternate arrangement fordischarging the capacitor 440. Various operational amplifiers 426provide input protection diodes. The capacitive plate element 432 whichis coupled with the output of the operational amplifier 426 is switchedto be grounded. Charge stored on the capacitor is then dissipatedthrough the protection diodes of the operational amplifier 426. In someembodiments resistive elements are provided to limit instantaneouscurrent during discharge.

The operational amplifier 426 includes supply connections to providepower to the operational amplifier 426. The capacitor 440 is reset, insome examples, by grounding the supply connections of the operationalamplifier 426. Charge stored on the capacitor 440 is then dissipatedthrough the internal diode structures of the operational amplifier. Insome embodiments resistive elements are incorporated to control the rateof change of voltage to limit instantaneous current.

In another embodiment, the capacitor 440 is reset by partially or fullyreversing the supply connections of the operational amplifier 426.Charge stored on the capacitor 440 is then dissipated through theinternal diode structures of the operational amplifier. In someembodiments resistive elements are incorporated to control the rate ofchange of voltage to limit instantaneous current.

In still another embodiment, the spectrometer 100 further includes iongenerators in switched polarity cells. Instead of resetting thecapacitor 140, the ion generators are used to swing the capacitor to theopposite polarity.

While resetting of the capacitor 140 is described, it is also envisionedthat the detector 122 may also be used in an offset arrangement withoutresetting of the capacitor 140, as described in one embodiment, forexample, in U.S. Patent Application No. 61/654,426, entitled CapacitiveTransimpedance Amplifier With Offset, which was filed concurrently withand assigned to the assignee of the present application, incorporatedherein by reference in its entirety.

FIG. 5 illustrates an alternate embodiment of a spectrometer 500. Thespectrometer 500 includes substantially the same components as thespectrometer 100 of FIG. 1, however, the spectrometer 500 also includesa second collector 546, a second operational amplifier 548 and aresistive element 550 disposed in a feedback loop of the operationalamplifier 548. The resistive element 550 and the second collector 546are coupled at a junction 552 which is coupled with the inverting input554 of the second operational amplifier 548. The noninverting input 556of the second operational amplifier 548 is grounded.

In operation, a sample of interest is drawn into the ionization chamber510 and the ionization source 516 ionizes the sample. For a firstportion of time subsequent to the gate 114 being opened allowing ions totravel through the drift chamber 512, the ions are collected by thesecond collector 546. During this period of time, the first collector520 and its related circuitry are held in a reset state. Ionization bythe ionization source 516 typically results in a reactant ion peak (andresultant reactant ion peak current). Until this reactant ion peak haspassed, the second collector 546 and its associated circuitry are used.However, after the reactant ion peak, the first collector 520 and itsrelated circuitry are no longer held to reset and are used to monitorthe ion stream either alone or in combination with the second collector546. The described arrangement may be used in this way to magnifyselected portions of the ion spectrum.

FIG. 6 illustrates an alternate embodiment of a detector 622. In thisembodiment, the output of operational amplifier 626 is coupled with aresistive element 657. The resistive element 657 is coupled with aswitch 659 that, when closed, grounds the resistive element 657. Whenthe switch 659 is open, the resistive element 657 is coupled with thenon-inverting input of a second amplification element 661, In oneembodiment, an instrumentation amplifier or a second operationalamplifier. The output of the second operational amplifier 661 is coupledwith the feedback capacitor 640. Based on this configuration, the chargeacross the feedback capacitor 640 can be changed independently of theexisting state of the system and independently of the input signal. Whenthe switch 659 is closed, the voltage at the capacitive plate element632 connected to the second amplification element 661 can be driven toany level within the supply voltages of the amplification element. Theopposite plate of the capacitor 640 is claimed near ground byback-to-back diodes 663. While the diodes 663 are shown as separateelements, In one embodiment, these diodes 663 are incorporated into theinput circuit of the first amplification element 626. Thus, In oneembodiment, the capacitor 640 may be reset without additional componentsor additional connections to the summing junction node 642.

The dielectric 128 and the components described on the side of thedielectric 128 opposite the collector 120 may be arranged in variousembodiments inside or outside of the drift chamber 112 and the housing102. It is envisioned that in some embodiments the summing junction ofthe integrator, the dielectric, etc., may be located inside of thehousing 102 with these elements being suitably shielded by any means.

While the capacitive elements in the above described embodiment aredescribed in terms of a parallel plate-type capacitor, use of othercapacitive arrangements are also envisioned. Additionally, while in theembodiment described the PCB acts as the dielectric 128, it is alsoenvisioned that the PCB may be used in conjunction with otherconstructional techniques to provide an air gap between the capacitiveplate element 132 and the collector 120.

Additionally, while the amplification circuit 126 is illustratedschematically in the figures, it is envisioned that the amplificationcircuit 126 may be supported by the PCB 128. In other embodiments, theamplification circuit 126 may be separate from the dielectric.

Embodiments of detectors including capacitive transimpedance amplifiersmay avoid or reduce thermal noise, providing a low noise signal.

In one embodiment, a transimpedance amplifier may provide shielding fromexternal noise sources and avoid noise introduction. In anotherembodiment, a transimpedance amplifier may provide broad bandwidth. Inanother embodiment, a transimpedance amplifier may avoid electricalleakage.

While the integrated capacitive detector is described above incombination with a particular embodiment of an IMS, such IMS that areconfigured to operate at ambient pressure, it is envisioned thatembodiments of the integrated capacitive detector will be utilized withvarious different spectrometer arrangements, including FAIMS and DMS.Exemplary spectrometry apparatus with which it is envisioned thatembodiments of integrated capacitive detectors may be used aredisclosed, for example, in U.S. Pat. No. 6,051,832 to Bradshaw et al.,U.S. Pat. No. 6,255,623 to Turner et al., U.S. Pat. No. 5,952,652 toTaylor et al., U.S. Pat. No. 4,551,624 to Spangler et al., U.S. Pat. No.6,459,079 to Machlinski et al., and U.S. Pat. No. 6,495,824 to Atkinson,the disclosure of each of which is incorporated herein, in its entirety,by reference.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) is to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

In additional embodiments, a variety of analytical devices may make useof the structures, techniques, approaches, and so on described herein.Thus, although an IMS device is described throughout this document, avariety of analytical instruments may make use of the describedtechniques, approaches, structures, and so on. These devices may beconfigured with limited functionality (e.g., thin devices) or withrobust functionality (e.g., thick devices). Thus, a device'sfunctionality may relate to the device's software or hardware resources,e.g., processing power, memory (e.g., data storage capability),analytical ability, and so on. For example, the corona source can alsobe used in other types of spectrometry involving an ionization processsuch as mass spectrometers (“MS”).

While reference is made to amplifiers and amplification elements, it isnot intended that an amplifier or an amplification element be limited toa single element. Instead, it is envisioned that these terms may in someembodiments encompass circuits including multiple elements, integratedcircuits, or any other arrangement suitable for amplification.

Although this disclosure has described embodiments in a structuralmanner, the structure and its structural and/or functional equivalentscan perform methods.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

Although the invention has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the invention defined in the appended claims is not necessarilylimited to the specific features or acts described. Rather, the specificfeatures and acts are disclosed as example forms of implementing theclaimed invention.

What is claimed is:
 1. A spectrometer comprising: a detector including:a collector having a first side and a second side, the first side beingconfigured to detect ions that drifted toward the collector; adielectric element proximate the second side; an amplifier having aninput and an output; and a capacitive plate element proximate thedielectric element and opposite the collector, the capacitive plateelement being coupled with the output of the amplifier.
 2. Thespectrometer of claim 1, wherein the dielectric comprises a printedcircuit board.
 3. The spectrometer of claim 1 or 2, wherein thecollector, the dielectric element, and the capacitive plate elementfunction as a capacitor in the feedback loop of the amplifier.
 4. Thespectrometer of any preceding claim wherein, the collector is coupledwith the input of the amplifier, so the amplifier, the collector, thedielectric element, and the capacitive plate element form a capacitivetransimpedance amplifier.
 5. The spectrometer of claim 3 or 4, whereinthe capacitive plate element, the dielectric, and the collector comprisean integrator circuit configured to integrate ion current from thecollector as a voltage.
 6. The spectrometer of any of claims 3 to 5,further comprising a reset circuit, coupled with the capacitor, that isconfigured to selectively reset the capacitor.
 7. The spectrometer ofany of claims 3 to 6, wherein the amplifier comprises an operationalamplifier; and wherein the capacitor is configured to be selectivelyreset by discharging through diodes of the operational amplifier.
 8. Thespectrometer of any preceding claim, comprising a guard ring surroundingthe collector proximate the dielectric.
 9. The spectrometer of anypreceding claim, wherein the dielectric comprises at least one of an airgap, printed circuit board, ceramic, thermoplastic, glass,polycarbonate, polyester, polystyrene, polypropylene, or PFTE.
 10. Thespectrometer of any preceding claim, wherein the spectrometer is an ionmobility spectrometer configured to operate substantially at ambientpressure.
 11. The spectrometer of any preceding claim, wherein thecapacitive plate element and the collector overlap over an area ofapproximately forty-four square millimeters.
 12. The spectrometer of anypreceding claim, further comprising a second collector coupled with atransimpedance amplifier configured to receive ions at least until anion peak has passed.
 13. A spectrometer comprising: a detectorcomprising: a collector configured to receive ions that drifted towardthe collector supported on a first side of a dielectric a plate elementdisposed on a second side of the dielectric opposite the first side inan overlapping configuration with the collector; and an amplifier havingan input and an output, the collector being coupled with the input, theplate element being coupled with the output.
 14. The spectrometer ofclaim 13, wherein the detector is configured as an integrator tointegrate an ion current from the collector into a voltage.
 15. Thespectrometer of claim 13 or 14, wherein the spectrometer comprises anion mobility spectrometer configured to operate substantially at ambientpressure.
 16. The spectrometer of any of claims 13 to 16, wherein thedielectric comprises a printed circuit board, and wherein the amplifieris supported by the printed circuit board.
 17. The spectrometer of anyof claims 13 to 16, wherein the overlapping portion of the collector andthe plate element and the dielectric are configured to act as acapacitor disposed in a feedback loop of the amplifier.
 18. Thespectrometer of any of claims 13 to 17 further comprising a resettingcircuit configured to selectively a resetting circuit configured toselectively reset the capacitor.
 19. The spectrometer of claim 17 or 18,wherein the amplifier includes at least one input protection diode; andwherein the resetting circuit includes a switching element and aresistive element, the switching element being selectively configured tocouple the plate element with the at least one input protection diode ofthe amplifier.
 20. A spectrometer comprising: a collector configured toreceive ions, the collector being arranged and configured as a firstplate of a capacitor; a dielectric proximate the collector; a plateconfigured as a second plate of a capacitor arranged opposite thecollector relative to the dielectric; and an amplification elementhaving an input, an output, and a feedback loop; wherein the capacitoris configured in the feedback loop.
 21. The spectrometer of claim 20,wherein the dielectric comprises at least one of air, polyimide,ceramic, thermoplastic, glass, polycarbonate, polyester, polystyrene,polypropylene, or PFTE.
 22. The spectrometer of claim 20 or 21, whereinthe collector, dielectric, plate, and amplification element are arrangedand configured as an integrator.
 23. The spectrometer of claim 22,wherein the integrator includes a summing junction, the spectrometerfurther comprising a resetting circuit configured to reset theintegrator without being directly coupled with the summing junction. 24.The spectrometer of any preceding claim wherein the collector isdisposed towards an end of a drift tube of the spectrometer forcollecting ions from the drift tube.